The synthesis of 3,5-disubstituted cyclometalated iridium(III) hydrido complexes of the type [3,5-R2(POCOP)IrHX] (3,5-R2(POCOP) = κ3-C5HR2-2,6-(OPtBu2)2 with R = t-Bu, COOMe; X = Cl, H) is described. All complexes were investigated in the catalytic dehydrogenation of hydrazine borane and compared with the unsubstituted compounds [(POCOP)IrHX] (X = Cl, H). All catalysts are highly active and recyclable, clearly maintaining hydrogen production activity. The dehydrogenation products were structurally characterised by solid state NMR and FTIR spectroscopy. Experimental observations were complemented by a dispersion-corrected DFT study to rationalise the mechanism of hydrazine borane dehydrogenation.